(1) Field of the Invention
The present invention relates to an image forming apparatus in which images are formed selectively on one side or both sides of recording media based on the input image data.
(2) Description of the Related Art
A typical image forming apparatus for forming image on both sides of recording media has an intermediate tray which temporarily stores the recording media with an image on the first side thereon and is arranged in the recording media conveyance path extending from the paper feed potion to the paper output portion passing through the imaging portion. The recording media stored in the intermediate tray is inverted so as to be upside down and conveyed to the imaging portion so as to form an image on the second side. In such an image forming apparatus, recording media of which images are to be printed only on one side will be discharged to the paper output portion after passing through the imaging portion without being held in the intermediate tray.
In this way, the recording media of which images are to be printed on only one side is conveyed through the different path from that of the recording media of which images are to be printed on both sides. Therefore, in the image forming apparatus in which images can be formed selectively on one side or both sides of recording media based on the input image data, the conveyance path of the recording media needs to be switched selectively.
Accordingly, the conventional image forming apparatus is configured so that mode selection as to whether images are to be formed on one side or both sides of the recording media is designated before the start of image forming for a single medium or multiple recording media and then based on the selected mode a recording media conveyance path is selected. Therefore, in the conventional image forming apparatus, once an image forming operation is started, the recording media will be conveyed along the conveyance path designated based on the mode selected before the start of operation unless the operation is interrupted and the mode selection is changed.
Thus, in the conventional image forming apparatus, the designated mode at the start of operation, whichever it is, the duplex print mode or one-sided print mode, will be maintained during the image forming operation once it has been started. Therefore, if the image data to be supplied during an image forming operation started in the duplex print mode includes both the image data for forming images on both sides of the recording media and the image data for forming images on only one side of the recording media, the recording media of which images are to be formed only one side will also be conveyed along the same conveyance path as that of the recording media of which images are to be formed on both sides. Therefore, the recording media of which images are to be formed on only one side are compelled to be held in the intermediate tray and turned upside down, unnecessarily, causing a time loss and degradation of operational efficiency.
For example, referring to FIG. 1, in an image forming operation in the duplex print mode for image data of two sheets including image data G.sub.1 and G.sub.2 to be formed on both sides of the first recording medium P.sub.1 and image data G.sub.3 to be formed on one side of the second recording medium P.sub.2, the first recording medium P.sub.1 is fed from a paper feed portion 91 in a copier 90 and is formed on its first side with an image of image data G.sub.1 via an imaging portion 92, and then is stored in an intermediate tray 93. Whilst this first recording medium P.sub.1 is conveyed from intermediate tray 93 toward imaging portion 92 with its face upside down and is formed on its second side with an image of image data G.sub.2, the second recording medium P.sub.2 is fed from paper feed portion 91. After discharge of recording medium P.sub.1 to a paper output tray 94, an image of image data G.sub.3 is formed on the first side of recording medium P.sub.2 via imaging portion 92. The recording medium P.sub.2 of which the image of image data G.sub.3 has been formed on the first side is also held in intermediate tray 93 and fed again to imaging portion 92. However, no image data to be formed is present in imaging portion 92, so that the recording medium P.sub.2 is discharged to paper output tray 94 with no image formed on its second side. Thus the image forming operation is completed.
In this way, in conventional image forming apparatus 90, if the image data to be input during the image forming operation in the duplex printing mode includes image data G.sub.3 for forming an image on only one side of a recording medium, recording medium P.sub.2 on which the image of this image data G.sub.3 is formed is forced, wastefully, to be conveyed to paper output tray 94 by way of intermediate tray 93 and imaging portion 92 despite the fact that no image is formed through the second passage of imaging portion 92.
As a technique to eliminate the time loss during an image forming operation in the duplex printing mode, Japanese Patent Application Laid-Open Hei No.5-323720 discloses a configuration wherein when a recording medium different in size from that held in the intermediate tray is conveyed to the intermediate tray, the image formation for the second side of the recording medium being held in the intermediate tray is performed in preference and then the position of the aligning means of the intermediate tray is controlled and switched. However this publication has no reference to eliminating the time loss arising when the image data input during the image forming operation started in the duplex printing mode includes both the image data for forming images on both sides of recording media and the image data for forming images on only one side of recording media.